THE deployment of voiceover is a controversial matter. The great American screenwriting gurus tend to counsel staunchly against it.

In Spike Jonze's Adaptation, our protagonist Charlie Kaufman (Nicolas Cage) attends a seminar by the eminent Robert McKee (Brian Cox) in an effort to forge ahead with his troubled adaptation of Susan Orlean's The Orchid Thief. Charlie's angst-ridden interior monologue - "It is my weakness, my ultimate lack of conviction that brings me here. I should leave here right now" - is interrupted by McKee's contemptuous dismissal of the voice-over as narrative prop: "God help you if you use voice-over in yourwork . . . That's flaccid, sloppy writing. Any idiot can write a voice-over narration to explain the thoughts of a character."

One might equally argue that any idiot can write a how-to guide positing rules about three-act structures and character arcs in order to exploit the hopes of those not talented enough to make it by themselves.

But the thoughts of McKee and his ilk do have resonance in Hollywood, however, if only because they're repeated so often. McKee's rejection of voiceover works on Charlie Kaufman, whose inner voice falls silent for the remainder of Jonze's film.

Still, rules were made to be broken; and the voiceover refuses to die. The common injunction to "show, not tell" has proved unequal to screenwriters' yearning to jam in as many words as possible. Perhaps it's down to the fact that so many key sources of cinematic inspiration are larded with didactic first-person narration.

How much of an authority is Robert McKee when pitched against Wilder, Welles, Truffaut, Coppola, Malick and Scorsese? And the new generation of directors who have broken through from the artsy fringes to the classy end of the mainstream are no more resistent to the use of voiceover: consider the Coen Brothers, Sam Mendes, David Fincher, Wes Anderson, Michel Gondry and the aforementioned Spike Jonze.

It would be contrary to argue that all of these film-makers are cursed by flaccid, sloppy writing. Still, the practice does have a tendency to strip films of their mystery - ideas are forced home, rather than emerging through storytelling and characterisation. Permitting an omniscient outside observer or a privileged central character to comment on events is a way of guiding audience responses.

Naturally, the same function is served by every element of a film, from make-up to editing - but narration makes it explicit. In the current releases Domino, Lord of War and Revolver, ironies in the story are repeatedly pointed out in the voiceover, as if the writers don't trust us to draw our own conclusions.

In Domino (written by Richard Kelly, the wunderkind who wrote and directed Donnie Darko, but appears to have undergone a frontal lobotomy), the technique is especially intrusive. This film operates on a principle that one might profitably utilise in teaching a small child to read: it shows us something, labels it in on-screen text, and explains it to us in a loud voice, all at the same time. It's like Teletubbies with guns.

Couple this over-explanatory tendency with a frenetic sound mix that echoes and repeats banal phrases, and you have perhaps the most irritating use of voice-over in recent memory. "My name is Domino Harvey; I am a bounty hunter, " squeaks Keira Knightley. Or, "Heads you live, tails you die. 50-50 chance." Or, "There are three kinds of people in the world: the rich, the poor, and everybody in between." Sometimes, Domino gets a little more poetic: at one point, we're bafflingly informed that "reality eclipsed into the asphalt horizon". Sometimes she's terribly post-modern: "If you want to know what's true and what's not, f*** off. It's none of your business." Doubtless Domino would have been horrible without the voice-over, but we would have been spared the sense of a writer trying to pass off atrocious plotting as intelligent audience manipulation.

The same sort of didacticism applies to Lord of War, which backs the international adventures of naughty gun-runner Yuri Orlov (Nicolas Cage) with a voice-over reminding us of his moral culpability.

Elsewhere, as in Sin City, LA Confidential and Atom Egoyan's upcoming Where the Truth Lies, voice-over is employed to establish a definite genre affiliation; in these cases, the hard-boiled noir style.

Weighty thinking person's blockbusters such as American Beauty, Magnolia, 21 Grams and Million Dollar Baby use their narrations to lend a literary ponderousness to their stories. Other voice-overs (Fight Club, About a Boy, Bridget Jones's Diary, Mysterious Skin and Factotum) employ screeds from the film's literary source; still others (The Royal Tenebaums, Dogville, Amelie, 2046) are used to offer the sense of a literary source where none exists. The same gimmicks have informed American TV drama, where the knowing character narration is an epidemic.

Blame Sex and the City's Carrie Bradshaw, with her infernal "So, I got to thinking", or Desperate Housewives, with its commitment to explaining its most obvious plot points via a concluding voice-over: "Sometimes [velvety, ironic pause] it's the people closest to you [deranged over-emphasis] who can seem [weird melodic lilt] the very furthest away [self-satisfied purr]."

Robert McKee's prejudices might not bear analysis when pitted against film history; but trends suggest that he's got a point. There's a feeling, at present, of directors explaining too much: leaving too little space in their anxiety to prove their credentials or jazz up their storytelling. Films that allow their characters and imagery to speak for themselves - Ang Lee's Brokeback Mountain, which is based on a story by Annie Proulx but displays an awareness of the difference between cinematic and literary expression - now seem daring in their confidence. Sometimes, a story should be allowed to speak for itself.